Analysis of macromolecules in complex mixtures is challenging in many chemical and biochemical processes. For example, the analysis of a macromolecule product, e.g., a protein, typically involves first preparing a sample of a macromolecule from a complex mixture for analysis. FIG. 1 depicts an example of a macromolecule preparation process 100, which involves taking a sample from a complex liquid mixture, e.g. a biofluid in a bioreactor 102, separating a macromolecule 104 from other components in the mixture, and processing it to deliver a prepared macromolecule 104′ for analysis at analyzer 106.
Effective process control generally requires accurate and frequent sampling, yet sampling of an operating bioreactor is associated with numerous problems, particularly contamination from sampling. For example, a bioreactor fluid typically contains, in addition to the macromolecule of interest, components such as salts, nutrients, proteins, peptides, cells, cell components, biopolymers such as polysaccharides, and the like, all of which can confound analysis of the desired products. Sampling can introduce, for example, foreign or wild bacteria into a bioreactor, which can compete with the process bacteria in the bioreactor fluid. Other contaminants, e.g., chemical contaminants, can affect the growth of the process bacteria and can confound the analysis of process components in the bioreactor fluid. Contamination can also affect the sampling and analysis apparatus. For example, wild or process bacteria can colonize the sampling/analysis system, or the system can accumulate other components form the biofluid, e.g., as salts, nutrients, proteins, peptides, cells, cell components, biopolymers such as polysaccharides, all of which can confound analysis of the desired products. Additionally, frequent sampling can lead to build-up of the molecule or molecules being analyzed, which can lead to inaccuracy.
In particular, the problem of “backflow”, i.e., liquid cross-contamination, is especially difficult when interfacing two fluidic systems. Simple valve interfaces are inadequate because valves typically have crevices, joints, dead volume, and the like, where contaminants can lodge and accumulate, only to be released during another sample cycle. Additionally, valves can fail and allow undesirable contamination to occur before much measurable fluid has leaked. More complex valved interfaces are known, but some are costly and still suffer some of the problems of simple valve systems, while other examples are unsuitable for high pressure systems. Needle/septa interfaces are known to avoid backflow but have issues with septa lifetime, needle contamination during transfer, and are particularly troublesome for frequent, automated sampling of larger volumes. Furthermore, septa replacement itself opens the system for contamination.
FIG. 2 depicts typical steps that can be included in a macromolecule sample preparation process operating on a mixture 202. If the macromolecule is endogenous, i.e., is at least partly contained in cells, an optional lysing step 204 opens the cells so that the macromolecule 104 can be separated. Separation step 206 separates macromolecule 104 from rough components 207 and fine components 213. Rough components 207 can include, for example, insoluble cells 208, cellular fragments 210, soluble molecules 212 which are larger than macromolecule 104, and the like. Fine components 213 can include salts 214 and soluble molecules 215 that are smaller than macromolecule 104, and the like. The concentration of ions such as salts and hydrogen (i.e., pH) are adjusted in step 216. In step 218, the molecule can be denatured, i.e., can be heated and/or combined with a denaturing agent 220, producing prepared macromolecule 104′, which is typically at an increased concentration compared to macromolecule 104.
The various steps used for protein preparation in the prior art involve separation of components through labor intensive centrifugation or time-intensive matrix chromatography. Matrix chromatography uses expensive columns that can be prone to plugging when used with complex mixtures that include insoluble or precipitation-prone components. Centrifugation can be effective but can cause contamination problems as there is no way to readily isolate a sample from the environment during the various sample transfers typically employed, and the size of the centrifuge limits the amount of macromolecule that can be prepared at one time. Thus both methods are low throughput in terms of amount of macromolecule that can be prepared.
Additionally, both methods are low throughput in terms of the sampling frequency, as the time from sample extraction from a complex bioreactor mixture to analysis of the macromolecule can easily be four hours or more. Such a slow analysis time leads to poor optimization of reactor processes, resulting in lowered yields, increased costs, increased purification demands, and increased amounts of potentially hazardous biological waste. FIG. 3 depicts a hypothetical example comparing two sampling frequencies, wherein a lower sampling frequency versus time (squares) can miss details in the level of a desired macromolecule versus time (solid line) in a reaction mixture, compared to a higher sampling frequency (circles). For example, the lower sampling frequency can miss the maximum macromolecular concentration 302 by measuring only lower concentration 300.
Electrophoresis is an analytical technique commonly used to separate molecular species, e.g., peptides, proteins, oligonucleotides, small organic molecules, and the like. The molecules, in a separation medium, e.g., a solution or a gel matrix, separate under an applied electric field according to their electrophoretic mobility, which is related to the charge on each molecule, its size, and the viscosity of the separation medium.
FIG. 10 depicts the separation of a small molecule 1002 and a large molecule 1004, each with the same net positive charge, and a small negatively charged molecule 1006. Application of electric field 1008 causes differential motion of the charged molecules according to their electrophoretic mobilities, with cations 1002 and 1004 moving towards the anode 1010. In the ideal case, the anions 1006 move to the cathode 1012, though experimentally a phenomenon known as electroosmotic flow can reduce or reverse the anion to cathode motion.
In capillary electrophoresis (CE), the separation is performed in a capillary tube having an internal diameter on the order of tens to hundreds of micrometers. In such small tubes the heat generated by the electric field is easily dissipated, so that high electrical fields can be used, leading to fast separations. FIG. 11 depicts a schematic of an electrophoresis apparatus 1100. An inlet vessel 1102 and an outlet vessel 1104 are connected by a capillary column 1106. The vessels and the capillary contain a buffer with an appropriate electrolyte. Upon loading a sample containing the analyte of interest at the inlet vessel, an electric field provided by a high voltage power supply 1108 causes the various molecules in the sample to separate, whereupon they can be detected by a detector 1110.
While capillary electrophoresis is powerful and versatile, it is sensitive to variations in acidity (pH), ionic strength, temperature, viscosity and other physical characteristics of the mixture, properties intrinsic to the analytes being studied, and contamination issues. Furthermore, small capillaries are physically fragile and are not suited to high-throughput separations, being easily plugged from the many macromolecules and debris in a complex mixture. In particular, rapid separation and analysis of macromolecules from complex liquid mixtures, for example, during the analysis of proteins produced in a bioreactor, is especially challenging.
In one example of CE technology a fragile, small diameter capillary is repeatedly applied by robotics to a series of distinct inlet vials. The repetitive motion can easily break the CE column. Column replacement requires time-consuming recalibration of the robotic motion. Another example of CE technology employs microchannels etched into a glass chip. While this hardware is durable, the separation efficiency is limited by the length of CE channel that can be fabricated on a chip. Attempts to extend the channel length by increasing channel density on a chip generally restrict high electric fields from use, increasing separation time. Also, the throughput of this technique is limited. Furthermore, sample transfer as practiced in both the robotic capillary technique and the chip technique expose the analytic solution to undesirable environmental contamination.